Projections of non-exhaust emissions from brake wear across Japan for 2020-2050

The concerns regarding the detrimental impacts of the increasing proportion of non-exhaust emissions are growing, even though there is a decrease in exhaust emissions from vehicles worldwide. Brake wear is a source of non-exhaust emissions. Despite the high density of traffic in Japan, the emission from brake wear has rarely been the target of studies. The objectives of this study are to estimate the environmental concentrations of copper (Cu) and antimony (Sb) released from brake wear in Japan and compare these concentrations on an annual basis (from 2020 to 2050). The Cu content in brake pads is estimated to decrease greatly from 2021 to 2025, whereas the Sb content is estimated to a moderate level by 2050. In this study, we used an atmospheric dispersion model to predict the reduction in Cu and Sb concentrations emitted from vehicles; owing to the transition to electric vehicles equipped with regenerative brakes (which will generate fewer wear particles), the Cu and Sb emissions in 2050 will decrease by 98 and 89 %, respectively, compared to the emissions noted in 2020. However, the contribution of conventional and electric vehicles to Cu and Sb concentrations will reverse in 30 years, owing to the country's goal that electric passenger vehicles will account for 100 % of the new-vehicle sales by 2035. By 2050, the contribution of conventional vehicles to Cu and Sb concentrations will be only 1 and 3 %, respectively, which will be from conventional vehicles supplied to the market by 2034. Thus, based on the future estimates of the number of vehicles and the composition of their brake pads, we predicted the environmental concentrations of Cu and Sb released from brake wear. The projections presented in this study can serve future interdisciplinary studies on environmental pollution, anthropological emissions reduction, and sustainable development.